People enjoy swimming pools and spas for family activities, therapy, exercise, recreation, and relaxation. Swimming pools are less popular in colder climates, but still find uses in the summer months and indoor settings. In warmer climates, swimming pools are common in residences, hotels, resorts, and health clubs. Spas and hot tubs are found in all types of climates.
In general, people tend to enjoy pools and spas more when the water is relatively warm and pleasant. In swimming pools, some people find 75-80° F. water to be refreshing; other people find 85-90° F. water to be more comfortable. In spas, the water is generally even warmer in the 100-105° F. range. Depending on the time of year and outside air temperature, it is often necessary to heat the pool and spa water to the desired temperature. Most if not all spas and hot tubs include heaters to increase the temperature of the water to higher levels. In swimming pools, heaters have been used to extend the usable season and even make the pool a year-round attraction.
Swimming pool and spa heaters come in basic configurations where water is pumped from the main body of water, filtered, and then heated before returning to the pool. The most common types of filters are sand, diatomaceous earth, and cartridge. The filtered water is routed through heating chambers in the heater before returning to the main body of water. The heater can burn propane or natural gas as an open flame, which is applied directly to the heating chamber to increase the water temperature. Electricity can also be used as an energy source to power a heating element placed in proximity to the heating chamber. The heating element transfers heat to the heating chamber, which in turn increases the temperature of the return water to the pool or spa. In another embodiment, the return water is routed through solar collectors to increase its temperature.
A common problem with conventional heating systems for swimming pools and spas is that the user must either keep the water at the desired temperature at all times, even when the pool is not in use, or the user must allow for the time needed to increase the water temperature to a comfortable level. Keeping the water at a continuous warm temperature increases operating costs, wastes energy, and unnecessarily consumes natural resources. On the other hand, the process of increasing the water temperature to a comfortable level when it comes time to use the pool can take a considerable amount of time. If the pool water is initially at a low temperature, say 50° F., it may take many hours, or an entire day, to raise the temperature to say 80° F., depending on the energy transfer capacity of the heater and volume of pool water. The pool user must plan ahead to have the pool ready to use at the intended time. The requirement to plan ahead limits the spontaneity and enjoyment factor associated with using the pool or spa. Many times the user foregoes the use of the pool because it takes too long to heat the water or requires too much preparation effort.